N-type lead telluride

ABSTRACT

It is herein disclosed that the use of small amounts of scandium, yttrium, and the metals of the lanthanide series of the rare earths are effective N-type dopants for lead telluride.

Unite States Patent Kendall, Jr. et al.

[ 51 Mar. 28, 1972 [54] N-TYPE LEAD TELLURIDE [72] Inventors: Louis I'. Kendall, Jr., Scotia, N.Y.; James H. Bredt, Garrett Park, Md.

[73] Assignee: General Electric Company [22] Filed: Aug. 1, 1968 [21 App]. No.2 749,347

[52] US. Cl.. [51] Int. Cl. [5 8] Field 01 Search ....252/62.3, 136/238, 136/239 ..H0lv 1/18 ..252/62.3; 136/238, 239

[56] Reilerences Cited UNITED STATES PATENTS 3,285,019 11/1966 Henderson et a1 ..252/62.3 X

OTHER PUBLICATIONS Narasimhan et a1. Indian Journal of Physics," Vol. 41 (i 1) pages 803, 808- 810 and 812, (1967) [57] ABSTRACT It is herein disclosed that the use of small amounts of scandium, yttrium, and the metals of the lanthanide series of the rare earths are effective N-type dopants for lead telluride.

5 Claims, No Drawings N -TYPE LEAD TELLURIDE The invention disclosed herein was made in the course of or under a contract with the United States Air Force.

N-TYPE LEAD TELLURIDE This invention relates to semi-conductive materials and more particularly to N-type lead telluride semiconductive elements for use in the thermoelectric generation of power. It has been found that N-type lead telluride bodies having useful thermoelectric properties may be made using dopants of scandium, yttrium, and the metals of the lanthanide series rare earths.

More specifically, and as a disclosure of a working example, a single crystal body of N-type samarium doped lead telluride was produced in the following manner. The starting materials were 99.999 percent pure lead, 99.999 percent pure tellurium and about 99 percent pure samarium. Since it was desired to produce lead telluride containing about 1 mol percent samarium telluride, or a composition having the approximate formula of Pb Sm Te, 60.1 101 grams oflead, 37,3930 grams of tellurium and 0.4406 grams of samarium were placed in a pyrolytic graphite lined quartz tube which was then evacuated and sealed. The materials were then heated to about l,000 C. to form a melt and quenched. The ingot so-produced was placed in a conventional zone leveling apparatus in a vertical attitude in contact with a lead telluride seed crystal while a narrow molten zone produced by a resistance heater was passed from one end of the ingot to the other at a rate of 75 mils per hour, starting at the seed crystal-ingot interface.

After cooling, the ingot was removed and found to be composed of a single crystal produced by epitaxial growth from the seed crystal. A number of other lead telluride compositions were prepared in the same manner as set forth in the fol- The discrepancies between the nominal compositions and the analyzed single crystal compositions are believed to be caused by at least three factors: these ingots were produced by a zone leveling technique, the solid solubility limits of the several dopants in the lead telluride, and the position or location along the length of the ingot from which the sample for chemical analysis was taken. All these materials were found to be of the N-type and representative room temperature electrical properties were determined which are average values for from 4 to 5 test samples cut from the single crystal ingots which are set forth in the following table and compared to undoped pure lead telluride.

From Table II it is clear that the doped lead tellurides of the invention have significantly lower room temperature resistivities than undoped pure lead telluride. It will thus be apparent that useful thermoelectric materials comprising N-type lead telluride may be produced utilizing dopants selected from the metals scandium, yttrium and the lanthanide series of the rare earths.

While these N-type lead tellurides have been disclosed in the form of single crystals, it will be readily apparent to those skilled in the art that polycrystalline bodies may be readily formed from these materials and that, if desired, such bodies may consist of more than a single phase. For these and other reasons, it is not intended that the invention shall be limited except as set forth in the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An N-type thermoelectric composition having a room temperature resistivity significantly lower than undoped pure lead telluride, consisting essentially of PbTe and a small amount of a dopant selected from the group consisting of scandium, yttrium and the metals of the lanthanide series rare earths having atomic numbers of 57 to 63 and 65 to 71, said dopant being present in an amount effective to produce the N- type electrical conductivity.

2. A composition as set forth in claim 1 wherein said dopant is scandium.

3. A composition as set forth in claim 1 wherein said dopant is yttrium.

4. A composition as set forth in claim 1 wherein said dopant is a lanthanide series rare earth metal.

5. A composition as set forth in claim 1 wherein said dopant is present in an amount up to about 4 mol percent. 

2. A composition as set forth in claim 1 wherein said dopant is scandium.
 3. A composition as set forth in claim 1 wherein said dopant is yttrium.
 4. A composition as set forth in claim 1 wherein said dopant is a lanthanide series rare earth metal.
 5. A composition as set forth in claim 1 wherein said dopant is present in an amount up to about 4 mol percent. 